This invention relates, in general, to semiconductor circuits and, more particularly, to a constant gain summing circuit.
Briefly, a constant gain summing circuit is used to accurately produce an output signal that represents the sum of one or more selected input signals. Such a summing circuit may be used in hard disk drive applications which require a tap summing network for a Partial Response, Maximum Likelihood, (PRML) mass storage data recovery channel.
Most, if not all, analog summer circuits are not capable of providing constant gain for each input signal and subsequently providing an accurate summed output signal. Prior summing circuits have had to resort to converting the input signals into digital form and using a digital adder to produce a summed signal. However, this digital form technique typically introduces undesirable clock delays when recovering data.
Hence there exists a need for a constant gain summing circuit that can produce the sum of several analog input signals while providing constant gain for each input signal present.